1. Field of the Invention
This invention relates to a collector shoe for use with an electrified conductor rail. More particularly, this invention relates to a segmented collector shoe assembly which includes a plurality of individually sprung collector shoe segments.
2. Description of the Related Art
Current collector shoe designs consist of a rigid collector shoe assembly mounted to a spring loaded arm. The arm is constructed such that it allows the shoe assembly to follow the conductor rail profile and adjust variations from parallel that the conductor rail may have relative to the running rail. These collector shoes are sized to have the appropriate amount of surface contact with the conductor rail to carry the electrical current required. Often they are sized for several hundred of amperes resulting in a long length of shoe.
A conductor rail cannot be manufactured perfectly straight and in some cases is required to be curved to follow the required path of the motorized equipment. When two rigid dissimilar surfaces are in contact, they will contact at the minimal number points to cause stability. Three points of contact are the minimum required for stability. The three points of contact are then subjected to a very high electrical current density causing each point to generate large amounts of heat. The heat then causes damage to the conductor rail and collector shoe ultimately resulting in shoe failure. This problem is particularly bad in installations where the equipment sits stationary for a period of time while drawing power.
A common current solution is to install multiple shoes along the rail to provide more points of contact to the conductor rail. This solution is undesirable because each shoe requires an additional mounting arm to be mounted to the equipment resulting in collector assemblies that grow incrementally in length for each collector that is installed. The long assemblies result in uneven load sharing between collectors. Also, the long collector assemblies reduce the amount of conductor rail length that can be used for movement because the space is occupied by collectors. Finally, the cost of the collector assembly is incrementally increased by the number of collectors installed.
Another problem with a rigid collector shoe is noted when it is used for signal or communication transmission while in motion. The three points of contact that were described above will continuously move from point to point and change along the collector shoe while the shoe is in motion along the conductor rail. Occasionally, as the collector shoe passes a joint in the conductor bar or even a spot of contamination or debris on the rail, the collector shoe resistance over the contact surface to the rail will rise to a point that the low voltage signal will not pass momentarily. This loss of signal can result in errors or faults between the equipment controls and drives. The typical solution is to install multiple shoes for redundancy. The intent being that at least one shoe will be making contact at any given time. The same undesirable characteristics of the multiple shoe solution apply to this situation as discussed hereinabove.